In the area of footwear intended for use by infants, who have weak ankles, and athletes, whose ankles may be weakened by fatigue, there have been numerous changes and modifications made in the heel area of shoes to reduce the tendency of the wearer's ankle to bend sideways upon impact of the heel at the start of each stride. To reduce excessive bending, known as pronation when the foot deflects inwardly, the most common direction, and known as supination when it bends in the opposite direction, and to reduce the incidence of the resulting injury, various means have been proposed.
The concept involved is to increase the lateral stability of the shoe to prevent it from bending about its roll axis. This has been done by making the U-shaped periphery of the heel area of a shoe of a harder rubber or like material than the middle of the heel area, or by the equivalent means of placing pins or plugs of harder material around the heel periphery area of a shoe layer such as a midsole or heel wedge area, or by the inverse method of placing either holes or plugs of softer material in the center of the heel area of such a layer. Stiff plastic plates have been placed horizontally between layers at the heel of a shoe to reduce differential compression of inner and outer heel edges upon heel impact. Cardboard inserts or insoles have been provided with a pattern of slits at the center of the heel area, such as slits in a radial pattern from a common center, to make the center less stiff than the sides.
Also, in an attempt to insure that the shoe itself impacts squarely, which may help maintain the wearer's ankle in the proper locked position, the heel area of the outsole has been extended sideways and rearward beyond the body of the shoe, forming a large flat initial impact area. The high stresses imposed on the shoe structure itself by this extension tend to cause delamination of layers of the shoe structure. To avoid this delamination, such shoes include an upward extension of the rubber of the outsole around the periphery of the heel area, bonded to the heel wedge or lift layer and to the midsole layer, and terminating with a thin, blended edge at the heel counter pocket. This upward extension is tapered in thickness, being thickest where stresses are highest, adjacent the outward extension of the sole, and thinnest where it blends into the heel counter pocket. It is partially glued to the heel counter pocket, but no adhesive is applied to its uppermost extension, to avoid extrusion of adhesive over the blend line and extends only far enough to resist outsole and heel lift or wedge delaminating forces and provide a smooth blending into the surface of the heel counter pocket. To the extent that this upward extension may slightly increase lateral stability of the shoe heel, it detracts from the ability of the rear heel area of the shoe to absorb and cushion the shock of initial heel impact, causing fatigue and thus tending to increase the tendency toward injurious pronation of the wearer's ankle. The instant invention avoids these and other deficiencies of the prior art.